Spreaders are used to spread a variety of paving materials including, but not limited to, sand, asphalt and concrete across a roadbed or other area to be paved. When concrete is used as the paving material, the spreader receives the concrete from delivery trucks which transport the concrete to the paving site and spreads the concrete across the roadbed or other area to be paved as it slowly travels in a direction of paving. Following behind the spreader is a paver which vibrates, extrudes, consolidates and otherwise finishes the concrete which has been spread out across the roadbed by the spreader. The spreader maintains height and directional alignment using a sting line which is placed along the area to be paved at a fixed alignment which defines the elevation and direction of the desired paved surface.
Several components are common to all spreaders and include, but are not limited to, such items as a rectilinear chassis which supports various components of the spreader, two or four tracks depending upon the spreader design for propelling the spreader, conveyor belts for receiving the paving material from delivery trucks and delivering the paving material to a prepared roadbed, hoppers for receiving and funneling the paving material deposited by the delivery trucks onto the conveyor belts, a control panel and instrumentation for controlling operation of the spreader, a power engine for providing power to the spreader, a drive train and power transmission system for transmitting power from the power engine to the conveyor belts and other spreader components, and a hydraulic system for controlling the movement of the various components.
Spreaders are designed to travel either over a prepared roadbed or alongside the prepared roadbed on a haul road which is also used by delivery trucks to deliver the paving material to the spreader and by other construction equipment traveling around the paving project. Current spreaders which travel over the prepared roadbed incorporate a swinging "drawbridge" conveyor belt which extends from beneath the spreader chassis, out past a side of the spreader adjacent to the haul road, and out over the haul road. The conveyor belt swings to an upright position to allow delivery trucks to pass by the conveyor belt on the haul road and then swings down once a delivery truck has passed the conveyor belt. The delivery truck deposits the paving material onto the conveyor belt which transports the paving material beneath the spreader chassis where the paving material falls onto the prepared roadbed to form a mound. As the spreader travels in the paving direction, a rotating auger and a strike plate spread the paving material laterally toward the sides of the spreader thereby distributing the paving material across the width of the prepared roadbed leaving an area of deposited paving material.
Spreaders which travel over the prepared roadbed have an advantage over other spreaders in that they allow delivery trucks, and normal traffic in situations where the haul road is an existing road, to travel unobstructed along the haul road. These spreaders, however, have drawbacks specific to their design. First, the rotating auger is continually moving through abrasive paving materials as it spreads them across the prepared roadbed causing the auger to wear thereby necessitating relatively frequent replacements. Second, while the chassis of the spreader can be "telescoped" in and out to vary the width of the spreader, the auger and a strike plate are fixed and require substantial time, effort and cost to replace them with an appropriate sized replacement. Third, in the event that insufficient paving material is deposited beneath the spreader as the spreader travels in the paving direction, a shortage of paving material results with no means for spreading additional paving material in the deficient area. Lastly, the elevation of the conveyor belt is fixed relative to the chassis such that the spreader cannot be used for paving projects where there is a large difference between the elevation of the haul road and the prepared roadbed, which in the case of a reconstruction project or where a paved surface is being widened, can be as much a four feet or more.
Spreaders which travel along the haul road overcome the drawbacks of spreaders which travel over the prepared roadbed. Currently two types of spreaders which travel along the haul road exist. Both types incorporate swinging conveyor belts which have distinctly different placements and orientations with respect to the chassis as compared to "drawbridge" conveyor belts previously discussed. Instead of extending out over the haul road to receive paving materials and depositing them beneath the spreader, conveyor belts on these spreaders receive the paving material from delivery trucks which deposit the paving material either directly on top of the spreader or in a hopper in front of the spreader. The conveyor belts begin either beneath the spreader or in front of the spreader and extend out the side of the spreader or out the back of the spreader respectively. Both conveyor belts have the ability to swing back and forth across the prepared roadbed as the spreader moves in the paving direction thereby spreading the paving material across the prepared roadbed and eliminating the need for an auger and strike plate.
Since these spreaders travel on the haul road and drop the paving material from the swinging conveyor belt which are suspended over the prepared roadbed, they can accommodate wide variations between the prepared roadbed and the haul road. Furthermore, in the event that insufficient paving material is deposited on the prepared roadbed, the conveyor belt can be swung around to deposit additional paving material onto the deficient area. In the event that the conveyor belt can no longer reach the deficient area due to the spreader having traveled in the paving direction, the spreader can back up to reach the deficient area.
In a first type of spreader which travels on the haul road, the conveyor belt extends from beneath the chassis, out past the side of the spreader which is adjacent to the prepared roadbed, and over the prepared roadbed. As delivery trucks arrive at the spreader, they travel up a first ramp and onto the spreader where they deposit the paving material through an opening in the chassis and onto the conveyor belt. After depositing the paving material, the delivery trucks continue to travel in a forward direction down a second ramp and off the spreader. While this type of spreader overcomes the drawbacks of spreaders which travel over the prepared roadbed they create a different set of drawbacks. In addition to obstructing the haul road to normal traffic and construction equipment, these spreaders are extremely long, typically one hundred and twenty feet, and overly wide, typically sixteen feet, thereby making their transport expensive and cumbersome.
A second type of spreader which travels over the haul road incorporates a hopper attached to a front side of the spreader facing the paving direction. A first conveyor belt transports paving material, which has been deposited into the hopper by the delivery trucks, to a second conveyor belt at a rear side of the spreader. The second conveyor belt extends from the rear side of the spreader and swings out across the prepared roadbed. This type of spreader also overcomes the drawbacks of spreaders which travel over the prepared roadbed, however, this type of spreader requires at least a double width haul road in order to allow delivery trucks to travel around the spreader, deposit the paving material into the hopper, and depart from the spreader without obstructing other arriving delivery trucks.
To transport current spreaders from one paving site to another paving site, the spreaders are typically loaded onto a trailer and transported between sites. Loading the spreader onto the trailer requires that the main chassis of the spreader be raised off the ground, typically using hydraulic rams attached to the chassis, backing the trailer under the spreader and lowering the spreader onto the trailer. Although this approach is effective, it is cumbersome.
It would be advantageous, therefore, to devise a method and apparatus for spreading paving material across a prepared roadbed wherein a spreader travels over the prepared roadbed so that the haul road remains unobstructed. It would further be advantageous if such a method and apparatus eliminated the need for a rotating auger and strike plate and could accommodate wide differences between the elevation of the haul road and the elevation of the prepared roadbed. It would still further be advantageous if such a method and apparatus provided a method for depositing additional paving material in areas where the paving material has been deposited in an insufficient amount. It would yet further be advantageous if such an apparatus could be driven under its own power onto a trailer for transport between paving sites.